The present invention relates to the field of wireless communications in general and more particularly, to determining the location of wireless communication terminals.
Many communication terminals, such as cellular communication terminals, personal digital assistants (PDAs), laptop computers, and the like, are now equipped with Global Positioning System (GPS) receivers to enable users to determine their location. GPS is a space-based radio triangulation system using a constellation of satellites in orbit around the Earth. A GPS receiver triangulates its position based on timing of radio signals it receives from various ones of the satellites and the known location of those satellites.
Determining the position of a GPS receiver typically requires the acquisition of a set of navigational parameters from the navigational data signals of four or more GPS satellites. The algorithms that are used to acquire GPS signals and determine position therefrom are complex and require substantial processing throughput. The process of monitoring GPS signals can be significantly affected by environmental factors. For example, GPS signals that may be easily acquired in the open typically become harder or impossible to acquire when a receiver is within a building, a vehicle, and/or under foliage.
The process to acquire GPS signals can take several minutes depending upon how much acquisition information a GPS receiver has initially. In order to improve GPS receiver performance, techniques have been developed to provide GPS receivers with GPS acquisition assistance information, e.g., time and position estimates, satellite ephemeris and clock information, and a visible satellite list from a terrestrial cellular communication system, which can enable a GPS receiver to expedite its acquisition of GPS signals and associated position determination.
As can be appreciated, incorporating a GPS receiver and associated processing circuitry into a wireless terminal can greatly increase its cost and complexity. This cost and complexity further increases when the wireless terminal is further configured to receive and use GPS acquisition assistance information from a cellular communication system.